This invention is generally directed to developer compositions, and more specifically, the present invention is directed to toner compositions, including magnetic toner compositions, containing therein certain charge enhancing additives, which impart a positive charge to the toner resin particles. Compositions with the specific quaternary ammonium sulfate charge enhancing additives of the present invention are useful for causing the development of electrostatic latent images, including color images. More specifically, positively charged toner compositions having incorporated therein these charge enhancing additives are particularly useful in electrostatographic imaging systems with a Viton coated fuser roll, since the sulfate additives involved do not react substantially with Viton, causing undesirable decomposition thereof, thereby adversely affecting image quality. Moreover, the toner compositions of the present invention with the charge enhancing additives therein, particularly distearyl dimethyl ammonium methyl sulfate, (DDAMS), can be desirably prepared by extrusion toner processing.
Developer compositions containing charge enhancing additives, including those which impart a positive charge to the toner resin, are well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935, the use of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. In accordance with the disclosure of this patent, specific quaternary ammonium salts when incorporated into a toner material provided a composition which exhibited relatively high uniform stable net toner charge when mixed with a suitable carrier vehicle, and this material also exhibited a minimum amount of toner throw off. Also, there is disclosed in U.S. Pat. No. 4,338,390 developer and toner compositions having incorporated therein as charge enhancing additives organic sulfate and sulfonate compositions. Other patents disclosing toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014 and 4,394,430.
Further, there is disclosed in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica.
Moreover, there is disclosed in U.S. Pat. No. 4,298,672 positively charged toner compositions containing resin particles, and pigment particles, and as a charge enhancing additive alkyl pyridinium compounds and their hydrates of the formula as detailed in column 3, beginning at line 14. Examples of alkyl pyridinium compounds disclosed include cetyl pyridinium chloride. While the developer compositions disclosed in the U.S. Pat. No. 4,298,672 are sufficient for their intended purposes, it appears that the alkyl pyridinium compounds involved react with the polymer contained on Viton fuser rolls causing decomposition thereof. Also, several of the other charge control agents disclosed in the prior art interact with certain fuser rolls, such as Viton fuser rolls, used in electrostatographic systems. This interaction causes the fuser to be adversely affected resulting in the deterioration of image quality. For example, Viton fuser rolls discolor and turn black, develop multiple surface cracks and harden when certain charge control additive compounds are contained in the toner mixture.
One Viton fuser roll selected for use in electrostatographic copying machines is comprised of a soft roll fabricated from lead oxide, and duPont Viton E-430 resin, vinylidene fluoride hexafluoropropylene copolymer. This roll contains approximately 15 parts of lead oxide, and 100 parts of Viton E-430, which mixture is blended and cured on the roll substrate at elevated temperatures. Apparently the function of the lead oxide is to retain the liberated hydrogen fluoride gas, assist in the crosslinking reaction, contribute to degradative stability, generate unsaturation by dehydrofluorination for crosslinking, and to provide release mechanisms for the toner composition. Excellent image quality has been obtained with Viton fuser rolls, however, in some instances there results a toner fuser compatibility problem when charge control agents are part of the toner mixture. For example, it appears that certain specific charge control additives, such as quaternary ammonium compounds, and alkyl pyridinium compounds, including cetyl pyridinium chloride, react with the Viton of the Viton fuser roll. For example, cetyl pyridinium chloride when part of the toner mixture appears to be catalytically decomposed by the lead oxide contained in the fuser roll resulting in a highly unsaturated compound, which polymerizes and condenses with the unsaturated Viton E-430 material. In view of this, the Viton fuser roll turns black, develops multiple surface cracks, and the surface thereof hardens thereby resulting in image quality deterioration.
Toner compositions with many of the above described charge enhancing additives are useful for causing the development of images formed on layered photoresponsive imaging devices comprised of generating layers and transport layers. These devices are charged negatively, rather than positively as is usually the situation with selenium photoreceptors, thus a toner composition which is positively charged is required in order that the toner particles may be suitably attracted to the electronstatic latent image contained on the photoreceptor surface. In view of this, efforts have been devoted to obtaining developer compositions containing toner resins which are positively charged. Thus, while many charge control additives are known, for this purpose there continues to be a need for new additives. Specifically, there continues to be a need for additives which will not interact with Viton type fuser rolls. Moreover, there continues to be a need for positively charged toner and developer compositions possessing rapid admix charging characteristics. Further, there continues to be a need for new charge enhancing additives which can be economically prepared. Additionally, there is a need for substantially nontoxic charge enhancing additives, and a need for charge enhancing additives which can be easily and permanently dispersed in toner resin particles. Also, there is a need for toner compositions with charge stability which can be desirably obtained by extrusion toner processing.